1. Field of the Invention
The invention uses thiourea compounds to inhibit bacterial adhesion to submergible or submerged surfaces, particularly those surfaces within an aqueous system. The invention also relates to methods and compositions for controlling biological fouling.
2. Description of Related Art
Microorganisms adhere to a wide variety of surfaces, particularly surfaces in contact with aqueous fluids which provide a suitable environment for microbial growth. For example, microorganisms are known to adhere to ship hulls, marine structures, teeth, medical implants, cooling towers, and heat exchangers. Adhering to such submerged or submergible surfaces, microorganisms may foul the surface or cause it to deteriorate.
In mammals, (e.g., humans, livestock, pets), microorganisms adhered to a surface may lead to health problems. Plaque, for example, results from microorganisms adhering to the surfaces of teeth. Medical implants with unwanted microorganisms adhered to their surfaces often become crusted over and must be replaced.
Scientific studies have shown that the first stage of biofouling in aqueous systems is generally the formation of a thin biofilm on submerged or submergible surfaces, i.e., surfaces exposed to the aqueous system. Attaching to and colonizing on a submerged surface, microorganisms such as bacteria, are generally thought to form the biofilm and modify the surface to favor the development of the more complex community of organisms that make up the advanced biofouling of the aqueous system and its submerged surfaces. A general review of the mechanisms of the importance of biofilm as the initial stage in biofouling is given by C. A. Kent in "Biological Fouling: Basic Science and Models" (in Melo, L. F., Bott, T. R., Bernardo, C. A. (eds.), Fouling Science and Technology, NATO ASI Series, Series E, Applied Sciences: No. 145, Kluwer Acad. Publishers, Dordrecht, The Netherlands, 1988). Other literature references include M. Fletcher and G. I. Loeb, Appl. Environ. Microbiol. 37 (1979) 67-72; M. Humphries et. al., FEMS Microbiology Ecology 38 (1986) 299-308; and M. Humphries et. al., FEMS Microbiology Letters 42 (1987) 91-101.
Biofouling, or biological fouling, is a persistent nuisance or problem in a wide varieties of aqueous systems. Biofouling, both microbiological and macro biological fouling, is caused by the buildup of microorganisms, macro organisms, extracellular substances, and dirt and debris that become trapped in the biomass. The organisms involved include microorganisms such as bacteria, fungi, yeasts, algae, diatoms, protozoa, and macro organisms such as macro algae, barnacles, and small mollusks like Asiatic clams or Zebra Mussels.
Another objectionable biofouling phenomenon occurring in aqueous systems, particularly in aqueous industrial process fluids, is slime formation. Slime formation can occur in fresh, brackish or salt water systems. Slime consists of matted deposits of microorganisms, fibers and debris. It may be stringy, pasty, rubbery, tapioca-like, or hard, and have a characteristic, undesirable odor that is different from that of the aqueous system in which it formed. The microorganisms involved in slime formation are primarily different species of spore-forming and nonspore-forming bacteria, particularly capsulated forms of bacteria which secrete gelatinous substances that envelop or encase the cells. Slime microorganisms also include filamentous bacteria, filamentous fungi of the mold type, yeast, and yeast-like organisms.
Biofouling, which often degrades an aqueous system, may manifest itself as a variety of problems, such as loss of viscosity, gas formation, objectionable odors, decreased pH, color change, and gelling. Additionally, degradation of an aqueous system can cause fouling of the related water-handling system, which may include, for example, cooling towers, pumps, heat exchangers, and pipelines, heating systems, scrubbing systems, and other similar systems.
Biofouling can have a direct adverse economic impact when it occurs in industrial process waters, for example in cooling waters, metal working fluids, or other recirculating water systems such as those used in papermaking or textile manufacture. If not controlled, biological fouling of industrial process waters can interfere with process operations, lowering process efficiency, wasting energy, plugging the water-handling system, and even degrade product quality.
For example, cooling water systems used in power plants, refineries, chemical plants, air-conditioning systems, and other industrial operations frequently encounter biofouling problems. Airborne organisms entrained from cooling towers as well as waterborne organisms from the system's water supply commonly contaminate these aqueous systems. The water in such systems generally provides an excellent growth medium for these organisms. Aerobic and heliotropic organisms flourish in the towers. Other organisms grow in and colonize such areas as the tower sump, pipelines, heat exchangers, etc. If not controlled, the resulting biofouling can plug the towers, block pipelines, and coat heat-transfer surfaces with layers of slime and other biologic mats. This prevents proper operation, reduces cooling efficiency and, perhaps more importantly, increases the costs of the overall process.
Industrial processes subject to biofouling also include papermaking, the manufacture of pulp, paper, paperboard, etc. and textile manufacture, particularly water-laid non-woven textiles. These industrial processes generally recirculate large amounts of water under conditions which favor the growth of biofouling organisms.
Paper machines, for example, handle very large volumes of water in recirculating systems called "white water systems." The furnish to a paper machine typically contains only about 0.5% of fibrous and non-fibrous papermaking solids, which means that for each ton of paper almost 200 tons of water pass through the headbox. Most of this water recirculates in the white water system. White water systems provide excellent growth media for biofouling microorganisms. That growth can result in the formation of slime and other deposits in headboxes, waterlines, and papermaking equipment. Such biofouling not only can interfere with water and stock flows, but when loose, can cause spots, holes, and bad odors in the paper as well as web breaks--costly disruptions in paper machine operations.
Biofouling of recreational waters such as pools or spas or decorative waters such as ponds or fountains can severely detract from people's enjoyment of them. Biological fouling often results in objectional odors. More importantly, particularly in recreational waters, biofouling can degrade the water quality to such an extent that it becomes unfit for use and may even pose a health risk.
Sanitation waters, like industrial process waters and recreational waters, are also vulnerable to biofouling and its associated problems. Sanitation waters include toilet water, cistern water, septic water, and sewage treatment waters. Due to the nature of the waste contained in sanitation waters, these water systems are particularly susceptible to biofouling.
To control biofouling, the art has traditionally treated an affected water system with chemicals (biocides) in concentrations sufficient to kill or greatly inhibit the growth of biofouling organisms. See, e.g., U.S. Pat. Nos. 4,293,559 and 4,295,932. For example, chlorine gas and hypochlorite solutions made with the gas have long been added to water systems to kill or inhibit the growth of bacteria, fungi, algae, and other troublesome organisms. However, chlorine compounds may not only damage materials used for the construction of aqueous systems, they may also react with organic materials to form undesirable substances in effluent streams, such as carcinogenic chloromethanes and chlorinated dioxins. Certain organic compounds, such as methylenebisthiocyanate, dithiocarbamates, haloorganics, and quaternary ammonium surfactants, have also been used. While many of these are quite efficient in killing microorganisms or inhibiting their growth, they may also be toxic or harmful to humans, animals, or other non-target organisms.
One possible way to control the biofouling of aqueous systems, which include the associated submerged surfaces, would be to prevent or inhibit bacterial adhesion to submerged surfaces within the aqueous system. This can be done, of course, using microbicides which, however, generally suffer from some of the disadvantages mentioned above. As an alternative, the present invention provides methods and compositions useful to substantially inhibit bacterial adhesion to a submerged or submergible surface and in controlling biofouling of aqueous systems. The invention obviates the disadvantages of prior methods. Other advantages of this invention will become apparent from a reading of the specifications and appended claims.